The present invention relates to a slot machine of the type having a plurality of reels each having an annular series of spaced symbols on the peripheral surface thereof and, more particularly, to a slot machine in which the position of a reel either in rotation or at rest is determined according to regions into which the reel is divided and the number of pulse signals supplied to a pulse motor associated with the reel during rotation of the reel.
In recent slot machines, each reel is rotated by a pulse motor which is controlled by pulse signals provided by a microcomputer. The slot machine, which pays out tokens or coins according to predetermined prize-winning combinations of symbols on the reels in stopped position occurring on a specific line, is required to determine what combination of symbols has occurred on the specific line. In such slot machines having pulse motors as disclosed in, for instance, U.S. patent application Ser. No. 338,497, each reel is provided with a light shield plate which acts to reset the previous content of a pulse signal counting means to an initial content every time the light shield plate passes through a photo-detecting device at a fixed position in order to prevent the pulse motor from rotating without syncronism. Since the information of a certain relation between the symbols on each reel and the number of pulse signals is stored in a table memory, a symbol on a reel in stopped position is determined by reading the table memory while using the content of pulse signal counting means as an address signal.
As a reference point on a reel, in conventional slot machines, is detected by the use of a single light shield plate provided on the reel, the reel cannot be brought to a stop unless the light shield plate is detected. For this reason, a lamp is provided, which turns on after the detection of light shield plate at a fixed position, to indicate that a micro-computer is ready for receiving an instruction signal for stopping the reel from a push button switch. This procedure is time consuming, resulting in a prolonged duration for a game and hence in a reduction in the working ratio of the machine. Moreover, asynchronism of the pulse motor, if it occurs, can not be eliminated until the pulse motor has caused the reel to rotate fully one revolution, thus give rise to a difference between the counter-indicated and the actual stopped position of the reel.